/Engine/Plugins/Online/OnlineSubsystemUtils/Source/OnlineSubsystemUtils/Public/PartyBeaconState.h
Get an existing reservation containing a given party member
index of reservation, INDEX_NONE otherwise
virtual int32 GetExistingReservationContainingMember ( const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & PartyMember ) const